The Assessment Core (AC) coordinates and ensures quality-control for all aspects of the MARC core assessment protocol. Assessment, as defined here, includes (i) collection of blood samples (targeted families) or buccal brushings (all families) for DNA extraction, (ii) administration and scoring of diagnostic interviews, (iii) collection of questionnaire and checklist data, (iv) acquiring block-level census tract data to characterize the neighborhoods in which families are living, and (v) obtaining school system data to characterize the schools participants have attended. The AC is responsible for pretesting the core assessment protocol shared by MARC research projects, as well as conducting focus groups and interview and questionnaire pretests to fine-tune additional assessments targeted at improved understanding of ethnic differences in adolescent and young adult substance involvement. AC faculty and staff will take the lead in interviewer training sessions conducted on-site as well as assisting with training sessions for Australian staff. The AC is responsible for monitoring the quality of interviewer data that are collected, by (a) reviewing ('editing') completed interviews for completeness and adherence to protocol, (b) obtaining consultations from diagnosticians on coding issues when necessary, (c) providing rapid feedback to interviewers, allowing study participants to be recontacted to obtain clarification where necessary, (d) reviewing a random 5% sample of audiotapes from completed interviews to monitor adherence to protocol, and (c) leading biweekly interviewer sessions to address interviewer questions and problems. AC staff will be responsible for conducting an ongoing reliability study of the assessment protocol, in which families assessed initially by telephone diagnostic interview will be brought in for in person-interviews at the MARC facility (N=15 high- risk, N=15 control families per year, i.e. approximately 110 individuals per year). They will also be responsible for maintaining consistency of assessment approaches between the project where the field work is conducted in Australia and the other projects, by annual review of approximately 30 audiotapes from high risk and control participants, and by regular communication with the Australian project 4 coordinator. The AC will be responsible for DNA extraction, and for typing STR markers for non-paternity detection and confirmation of zygosity status of dizygotic twin pairs. Finally, it will provide a national resource for consultation on assessment and nosologic issues in genetic-epidemiologic studies.